Hand held mobile terminals, such as personal digital assistants (PDAs), have become widely accepted as personal and business organizational tools. Many users carry hand held mobile terminals on a daily basis. Accordingly, it is desired that housings for mobile terminals meet a number of criteria. A housing for a hand held mobile terminal should be aesthetically appealing. Moreover, the housing should be rugged to protect inner electronics from damage in the event of a drop. As mobile terminals become more and more powerful, a need for strength in the housing is at odds with a need to minimize volume occupied by the housing, and thus unavailable for packaging the electronics. Further, any latching mechanism used to hold the housing together should minimize any volume occupied and provide a secure latching system to prevent the disengagement of the housing parts.
Hand held mobile terminals are generally assembled by enclosing internal electrical components, such as a Central Processing Unit (CPU) board, display, keyboard, and internal wiring, within a housing made of plastic or another structural material. The enclosure is normally formed in two parts having an upper housing and a lower housing. The electronic components are mounted to one or both sides of the housing with or without a subframe. A subframe is employed to provide torsional rigidity to the structure. The display and sometimes the battery are also located within the enclosure. The display and the battery represent large masses that can impart undesirable impact loads to the CPU board during a drop event.
FIG. 1 depicts a conventional housing 100 for a hand held mobile terminal. The housing 100 comprises two halves 110 and 120. The two halves 110 and 120 are fastened together to contain electronics (not shown). Bosses 130 are included in the housing 100 such that fasteners 140 can penetrate both sides of the housing 100. The fasteners, or screws, 140 are inserted through bosses 130 on one half of the housing 100 through to the other half of the housing to provide the closing force needed to hold the assembly together. These features use volume that would otherwise be utilized for electrical components. Thus, the existence of bosses 130 reduces volumetric efficiency of the housing 100.
Additionally, the assembly of the components into the housing 100 requires several manufacturing processes. Before the housing 100 is fastened together, the CPU board, the display and other components must be assembled to a subframe, to the housing, or to some other subassembly. Such assembly steps are generally time consuming and expensive in manufacturing.
Further, the conventional housing assembly has poor torsional rigidity due to discontinuity of the housing surfaces at the mating band. Accordingly, stresses from deflections and impact loads during a drop are concentrated at the bosses 130. Housing failure is often attributed to boss failure caused by deflection and impact load stresses.